For the conversion setup you should always use the same (so find out what works best for you), and don't change it depending on the game. Also always use the same game as the source game so conversions stay consistent.
This way a scope with a FOV of X will be exactly the same in all games, which is the whole point. If you change source game or conversion setup you will not have any consistency.
Do note that the calculator does not cover every scenario, so if you have one preference for hipfire, one for 3rd person, one for ADS and one for scopes (all which does not convert between each other) you'll need to convert everything based on this. But this is more the exception, in most cases people prefer a unified source.